1052 D3000 new imprint Word template Vol 13, No 1 (2025) ISSN 2167-8677 (online) DOI 10.5195/d3000.2025.1052 http://dentistry3000.pitt.edu Tea Tree Oil Addition on Surface Roughness and Strength of High-Im- pact Acrylic Resin Material Mohammed Hameed Hassan, Aseel Mohammed Al-Khafaji College of Den*stry, University of Baghdad, Baghdad, Iraq Abstract Objec7ve: Polymethylmethacrylate (PMMA) is porous and rough in nature; this allows food to sOck to it and microbes to proliferate, maybe resulOng in oral disease. SelecOng the right denture cleanser is not enough to prevent all fungi from adhering to the denture or decrease roughness. The essenOal tea tree oil (TTO) possesses anOfungal, anOoxidant, and anObacte- rial characterisOcs. TTO will be used to study its effect on the surface roughness and impact strength of high-impact acrylic denture material aVer incorporaOon with TTO at concentra- Oons of 0%, 6%, and 9% by volume. Materials and Methods: 60 specimens were made and categorized into two groups. Each group consisted of 30 samples and was divided into three different concentraOons of TTO (0%, 6%, and 9% by volume). AVer 48 h incubaOon in disOlled water, all samples were assessed by two tests, the surface roughness test and the impact strength test. Atomic force microscopy (AFM) was used to prove the effect of TTO on the surface morphology at the nanoscale of high-impact acrylic. Results: Tea tree oil had a staOs- Ocally significant effect on surface roughness, which led to a decrease in surface roughness of high-impact acrylic. Also, TTO has a significant effect on the impact strength of high-impact acrylic at a 9% concentraOon, which causes a decrease in impact strength (P>0.05), but 6% TTO has a non-significant effect on high-impact acrylic (P<0.05). That means 6% TTO is the be_er concentraOon to use to improve the property of acrylic. Conclusion: The high-impact acrylic resin incorporated with the tea tree oil is effecOve. It appeared that 6% vol TTO will decrease the surface rough- ness and not significantly affect the im- pact strength of high-impact acrylic. Open Access Cita%on: Hassan MH, et al. (2025) Tea Tree Oil Addi%on on Surface Roughness and Strength of High-Impact Acrylic Resin Material. Den%stry 3000. 1:a001 doi:10.5195/d3000.2025.1052 Received: September 19, 2025 Accepted: September 24, 2025 Published: October 17, 2025 Copyright: ©2025 Hassan MH, et al. This is an open ac- cess ar%cle licensed under a Crea%ve Commons ARribu- %on Work 4.0 United States License. Email: Mohammed.Hasan2401m@codental.uobagh- dad.edu.iq Introduc)on Polymethyl methacrylate (PMMA) was the most widely utilized material for denture resin due to its aesthetically pleasing appear- ance, minimal water absorption, low toxicity, and excellent color stability [1]. PMMA is po- rous and rough in nature; this allows food ac- cumulation, discoloration of acrylic, compro- mised oral hygiene, reduced long-term suc- cess of prosthetic appliances, and the growth of microorganisms, which increases the risk of developing denture stomatitis, which is mostly caused by Candida albicans and can result in candidiasis. Therefore, it is essential to clean dentures after meals [2,3]. Also, the polymethyl methacrylate remained weak and unable of withstand the forces applied during chewing, and broken dentures are the most frequent complaint from denture users that dentists hear. These can be brought on by inadvertent prosthesis prognosis-in- duced overload oral stresses or due to the denture base prosthesis becoming exces- sively rigid with time because of chronic fail- ure induced by recurrent bite forces [4]. Re- search indicates that 67% of dentures suffer from degeneration after a few years of makeup [5]. To prevent fractures, high-im- pact PMMA was developed [6]. Particles of butadiene-styrene rubber are mixed with the powdered denture foundation compo- nents. The rubber is grafted with a methac- rylate group to provide a covalent connec- tion between the particles and the polymer network. PMMA with a high impact was de- veloped to resist fractures. The addition of a rubber phase as a butadiene-styrene copoly- mer has led to elevated costs and diminished transverse strength [7,8]. Some oils that are extracted from medicinal plants are utilized in biomaterials as a natural substitute that improves the properties of acrylic and has strong antifungal and antibacterial qualities. According to recent studies, plant oils with strong antifungal properties hold promise as Tea Tree Oil AddiOon on Surface Roughness and Strength of High-Impact Acrylic Resin Material Vol 13, No 1 (2025) DOI 10.5195/d3000.2025.1052 http://dentistry3000.pitt.edu 2 a treatment for stomatitis brought on by dentures [9,10]. In addition to their eco- nomic worth, the primary beneUits of utiliz- ing natural plant extracts include safety, bio- compatibility, and the absence of unwanted effects [2]. Research is being done on the therapeutic use of essential oils. Tea tree oil (TTO) is utilized in PMMA because it has an- tibacterial, antifungal, and antioxidant prop- erties [11,12]. The leaves of Melaleuca al- ternifolia, a plant from the area in Australia that produced tea tree oil (TTO), may be steam-distilled to obtain the oil. TTO was composed of several compounds, primarily hydrocarbons of monoterpene and sesquit- erpene and their alcohols. TTO possessed an- tiseptic and antibacterial properties, accord- ing to multiple studies [13]. The current study aimed to investigate the surface rough- ness and impact strength of high-impact acrylic's characteristics following its incor- poration with TTO. Materials and Methods Specimen grouping In this study, 60 specimens of the high-im- pact PMMA (Veracril® / Opti-cryl high im- pact, Newstetic, Colombia) were made; the concentration of TTO that is incorporated with high-impact heat-cure acrylic resin is 6 wt.% and 9 wt.% by volume, and the speci- mens will be created. A total of specimens of high-impact acrylic were carried out and cat- egorized into two sets. Each set includes 30 specimens spread among three different groups. (Group one: control; group two: 6% TTO; and group three: 9% TTO), including 10 specimens per group. Two tests are used in this study, including the impact strength test and the surface roughness test. Before the testing procedures, every specimen was in- cubated at 37°C for 48 hours after being stored in distilled water [14]. The Uirst control group was preserved in dis- tilled water with 0% TTO. The second group was the incorporation of high-impact acrylic with a 6% TTO. The third group was the incorporation of high-impact acrylic with a 9% TTO. A total of 60 specimens were used in the study. The measurement and mixing of high-im- pact PMMA components The preparation was performed for each percentage (0%, 6%, and 9%) of TTO by vol- ume (ml) to be able to withdraw with a mi- cropipette, while the powder of high-impact acrylic was calculated by using a digital bal- ance of 0.000 grams. TTO was added to the monomer of high-impact acrylic. The pro- portion of polymer to monomer (powder-to- liquid ratio of (2:1) by weight) P|L [15]. General test specimen preparation For surface roughness A carving machine was used to create a round stainless-steel mold and a cover for it. According to ISO 20795-1, 2013, the speci- men's thickness was 0.5 mm ± 0.1 mm, and its diameter was 50 mm ± 1 mm [16]. In both halves of the Ulask, the steel mold and lid were immersed in stone, as indicated in Fig- ure 1. Following the investment of the stain- less-steel mold and cover, the two compo- nents that made up the Ulask were then sep- arated. The testing was conducted using a proUilometer instrument, and the specimen was positioned on a level surface as shown in Figure 2. Three measurements were ob- tained for each specimen: one at the center and two equally from the center towards the boundaries on both sides. The average Ra values were computed in micrometers (μm). Figure 1. The steel mold and lid were im- mersed in stone inside Ulask. Figure 2. A profilometer instrument to measure the surface the roughness of speci- men. For the test of impact strength The designs were made using dimensions of 80 mm in length, 10 mm in width, and 4 mm in thickness in accordance with ISO 179 [17]. According to the manufacturer's recommen- dations (water/powder ratio of 25 mL/100 g), the type 4 dental stone (Zhermack®, It- aly) was prepared and put into the Ulask's lower section after it had been painted with separating media (IZO-SOL, Zhermack, It- aly). The mold and plastic design were then inserted into the stone and left to harden. Following the stone setting, the whole sur- face was painted with a separating sub- stance, including the stone and plastic pat- tern. Following that, the Ulask's top half was placed over its bottom half, Uilled with the new stone mixture, covered, and left to solid- ify. Therefore, the two halves of the Ulask were taken apart, and the designs were taken out, as shown in Figure 3. The speci- mens were then constructed, Uinished, and polished as shown in Figure 4. Figure 3. Flask and plastic mold for impact strength test. Figure 4. Finishing and polishing of impact strength specimen. The Charpy impact testing apparatus was utilized to perform the impact strength as- sessment, as shown in Figure 5. The Charpy impact strength of unnotched specimens was obtained using the following formula: Impact strength = E/B.D x 103 [18]. E is the energy absorbed for fracture meas- ured in joules. B represents the samples' width in millime- ters. D represents the thickness of the samples in millimeters. Tea Tree Oil AddiOon on Surface Roughness and Strength of High-Impact Acrylic Resin Material Vol 13, No 1 (2025) DOI 10.5195/d3000.2025.1052 http://dentistry3000.pitt.edu 3 The specimen was positioned vertically and impacted by a freely swinging pendulum of 5 joules, with the scale reading indicating the impact energy in joules. Figure 5. Specimen of impact test and Charpy impact testing machine. Atomic force microscope (AFM) Atomic Force Microscopy (AFM) is a na- noscale imaging technology that offers three-dimensional surface characterization with sub-nanometer resolution. It is exten- sively utilized in polymer research to assess morphological alterations, surface rough- ness, and nanomechanical characteristics following the modiUication or incorporation of plasticizers, Uillers, or essential oils [19]. AFM employs a sharp probe afUixed to a Ulex- ible cantilever to examine a surface. Inter- molecular interactions between the tip and the surface induce deUlections in the cantile- ver, which are documented to generate high- resolution maps (Figure 6). Figure 6. Atomic force microscope device. Statistical analysis Individual surface roughness and impact strength were calculated and compiled to de- termine the average and standard deviation for every category; IBM SPSS version 20 was employed. Tukey HSD and one-way ANOVA were used to compare the outcomes be- tween the groups. P < 0.05 was set as the sig- niUicant level. Results The group control demonstrated the great- est mean value (0.1431) upon examination of the pigmented specimens from each spe- ciUic group. The experimental groups came after that, with group 9% showing the mini- mal average value (0.0851). All the speci- mens utilized in the experiment showed a statistically signiUicant decrease in surface roughness, according to the Uindings shown in Table 1. Tables 2 to 6 summarize results for all com- parisons. Atomic force microscope (AFM) The AFM results show the mean surface roughness (sa) of the control group is 0.03308 µm (Figure 7), while the surface roughness after the addition of TTO at 6% is 0.024834 µm (Figure 8) and at 9% is 0.022768 µm (Figure 9). The incorpora- tion of TTO into the high-impact acrylic re- sults in a reduction in the surface roughness, as conUirmed by the AFM images. A rough- ness and irregular topography were ob- served in the control sample; however, the addition of 6% v/v and 9% v/v TTO resulted in a reduction in the surface irregularities. revealed that there was a change in the sur- face morphology. Figure 7. The results of the AFM surface topography analysis for the high-impact acrylic resin. Figure 8. AFM surface topography results for high-impact acrylic resin with 6% v/v TTO. Figure 9. AFM surface topography results for high-impact acrylic resin with 9% v/v TTO. Discussion The oral cavity experiences many alterations when utilizing an artiUicial prosthesis, poten- tially resulting in microbial colonization. In- dividuals who wear dentures are at an ele- vated risk of getting denture stomatitis, largely characterized by the presence of Can- dida albicans, which may result in the onset of candidiasis. This results from the rough- ness of the denture due to the nature of acrylic, leading to the adherence of microbes [2,20]. Natural tea tree oil signiUicantly decreased surface roughness when administered to acrylic resin, so the incorporation of TTO (6%, 9%) by volume into the high-impact acrylic in the experiment groups in compari- son to the control groups. TO has strong an- tioxidant and antimicrobial properties, in which the terpinen-4-ol has signiUicant ef- fects on the growth and function of Candida cells (Noumi Emira), which may change the permeability and membrane characteristics of fungal cells [21]. The impact strength values for the incorpo- ration of 6% TTO have no signiUicant differ- ence from the control (P > 0.05), whereas the incorporation of 9% TTO has a signiUicant ef- fect (P < 0.05) and decreases impact strength; therefore, 6% TTO is the better concentration to have been used because it has no effect on impact strength. These results may be attributed to the con- centration of supplementary oil, which func- tions as an elastomer for high-impact PMMA acrylic resin [22,23]. The incorporation of oil elastomer enhanced the material's energy absorption and reduced the likelihood of resin cracking, hence increasing the pros- thetic device's resistance to mechanical fail- ure [24]. Conclusion This study was performed to examine the surface roughness and impact strength of high-impact acrylic after incorporation with 6% and 9% TTO. The 6% and 9% of the oil group that incorporated with high-impact acrylic lead to a decrease in surface rough- ness of high-impact acrylic and a non-signif- icant effect on impact strength with 6% TTO, but with 9% TTO it causes a decrease in the impact strength; therefore, the recom- mended concentration of tea tree oil is 6% TTO. Conflict of Interest None. References Tea Tree Oil AddiOon on Surface Roughness and Strength of High-Impact Acrylic Resin Material Vol 13, No 1 (2025) DOI 10.5195/d3000.2025.1052 http://dentistry3000.pitt.edu 4 1. Noori ZS, Al-Khafaji AM, Dabaghi F. Effect of tea tree oil on candida adherence and surface roughness of heat-cure acrylic resin. Journal of Baghdad College of DenEstry. 2023 Dec 15;35(4):46-54. 2. Hammed SS, Al-Khafaji AM. Tea Tree Oil Effect on Dimensional Change and Detail ReproducEon of AddiEon Silicon Impression Material. Journal of DenEstry 3000.2024. 3. Pudhupalayam MuthukuY G, Singh MK, Palaniappan SK, Vijayananth K, Boonyasopon P, Mavinkere Rangappa S, Siengchin S. Sustainable polymer composites from agro and municipal green wastes: a comprehensive review of materials, properEes, and applicaEons. Journal of Material Cycles and Waste Management. 2025 Jul 15:1-22. 4. Al-Hiloh SA, Ismail IJ. A study of the effect of the addiEon of silanized zirconium oxide nanoparEcles on some properEes of high-impact heat-cured acrylic resin. Journal of Baghdad College of DenEstry. 2016;28(2):19-25. 5. Solhi L, Atai M, Nodehi A, Imani M, Ghaemi A, Khosravi K. Poly(acrylic acid)- graded montmorillonite as novel fillers for dental adhesives: synthesis, characterizaEon, and properEes of the adhesive. Dental materials. 2012 Apr 1;28(4):369-77. 6. Qanber LM, Hamad TI. Effect of plasma treatment on the bond of sod denture liner to convenEonal and high- impact acrylic denture materials. Journal of Baghdad College of DenEstry. 2021 Sep 15;33(3):9-17. 7. Meng TR, Laha MA. Physical properEes of four acrylic denture base resins. The Journal of Contemporary Dental PracEce. 2007 Mar 1;6(4):93-100. 8. Craig RG, O'Brien WJ, Powers JM. Dental materials: properEes and manipulaEon. (No Title). 2004. 9. Yahya YK, Al-Khafaji AM. The Impact of Tea Tree Oil on Bacillus subElis and the Surface Roughness of Type III Dental Stones. Journal of InternaEonal Dental and Medical Research. 2024 May 1;17(2):498- 506. 10. Al-Mashhadane FA. Tea Tree Oil: A New AnEfungal Against Candida Albicans Cells on Heat-Cured Acrylic Resin Denture Base Material. An in vitro study. Al-Rafidain Dental Journal. 2007 Dec 1;7(3):54-7. 11. Noori ZS, Al-Khafaji AM. EvaluaEon of the Effect of Tea Tree Oil Denture Cleanser on the ProperEes of Dental Polymers. Journal of Engineering. 2024 Nov 1;30(11):39-49. 12. Emira Noumi, MS. In vitro effect of Melaleuca alternifolia and Eucalyptus globulus essenEal oils on mycelia formaEon by oral Candida albicans strains. 13. Mondello F, De Bernardis F, Girolamo A, Salvatore G, Cassone A. In vitro and in vivo acEvity of tea tree oil against azole-suscepEble and -resistant human pathogenic yeasts. Journal of AnEmicrobial Chemotherapy. 2003 May 1;51(5):1223-9. 14. Salman TA, Khalaf HA. The influence of adding modified ZrO2-TiO2 nanoparEcles on certain physical and mechanical properEes of heat-polymerized acrylic resin. Journal of Baghdad College of DenEstry. 2015;27(3):33-9. 15. Hussain WA, Hashim FS. Effect of addiEves on impact strength of denture base resin. Iraqi Journal of Science. 2017:860-7. 16. Al-Khafagi KS, Mahmood W. EvaluaEon of the Transverse Strength and Surface Roughness ProperEes of High-Impact Polymethylmethacrylate ader Long-Term Submergence in Clove Oil SoluEon. Advanced Journal of Chemistry" (2025): 278-291. 17. Mawlood ZS, Naji GA. Influence of addiEon of bergamot essenEal oil on physico-mechanical behavior of heat-cured acrylic denture base. Int Med J. 2021 Jun 2;28(1):21-5. 18. NIMER AM, JASSIM RK. Studying the Effect of Ascorbic Acid on Some ProperEes of Autoclaved and Heat-Cured Denture Base Material. 19. Liang X. VisualizaEon of nanomechanical properEes of polymer composites using atomic force microscopy. Polymer Journal. 2023 Sep;55(9):913-20 20. Dhir G. Physical ProperEes of Denture Base Resins Resistant to Candidiasis. 21. Emira N, Mejdi S, Aouni M. In vitro acEvity of Melaleuca alternifolia (tea tree) and Eucalyptus globulus essenEal oils on oral Candida biofilm formaEon on polymethylmethacrylate. J. Med. Plants Res. 2013 Jun 12; 7 (20): 1461-6. 22. Faot F, Costa MA, Cury AA, Garcia RC. Impact strength and fracture morphology of denture acrylic resins. The Journal of ProstheEc DenEstry. 2006 Nov 1;96(5):367- 73. 23. Alarifi, IM. A comprehensive review on advancements of elastomers for engineering applicaEons. Advanced Industrial and Engineering Polymer Research. 2023 Oct 1;6(4):451-64. 24. Al-Badr RJ, Al-Huwaizi HF. Effect of tea tree, Thymus vulgaris, and Nigella saEva oils on the eliminaEon of Enterococcus faecalis (in vitro study). Journal of Baghdad College of DenEstry. 2017 Mar 13;29(1):55- 62. Tea Tree Oil AddiOon on Surface Roughness and Strength of High-Impact Acrylic Resin Material Vol 13, No 1 (2025) DOI 10.5195/d3000.2025.1052 http://dentistry3000.pitt.edu 5 Table 1. Descriptive statistics for test of surface roughness. Sample N Mean Standard Devia- tion Standard Er- ror Minimum Maximum Control 10 0.1431 0.004841 0.001531 0.136 0.149 6% tea tree oil 10 0.1033 0.003713 0.001174 0.097 0.108 9% tea tree oil 10 0.0851 0.002807 0.000888 0.081 0.089 Total 30 0.1105 0.024916 0.004549 0.081 0.149 Table 2. ANOVA analysis of surface roughness test. Sample Sum of Squares Degrees of freedom Mean Square F p-value Between Groups 0.018 2 0.009 585.286 0.000 Within Groups 0.0 27 0.0 Total 0.018 29 Table 3. Comparative analysis of surface roughness among groups utilizing Tukey HSD. (I) (J) (I-J) Mean Difference Standard Error p-value Control 6% TTO 0.398 0.001734 0.000 9% TTO 0.058 0.001734 0.000 6% TTO 9% TTO -0.0182 0.001734 0.000 Tea Tree Oil AddiOon on Surface Roughness and Strength of High-Impact Acrylic Resin Material Vol 13, No 1 (2025) DOI 10.5195/d3000.2025.1052 http://dentistry3000.pitt.edu 6 Table 4. Descriptive statistics for the impact strength. Sample N Mean Standard Devia- tion Standard Er- ror Minimum Maximum Control 10 13.925 0.23717 0.075 13.5 14.25 6% tea tree oil 10 13.8 0.2582 0.08165 13.5 14.25 9% tea tree oil 10 13.375 0.3385 0.10704 13 13.75 Table 5. ANOVA test for impact strength test. Sample Sum of Squares Degrees of freedom Mean Square F p-value Between Groups 1.663 2 0.831 10.5 0.000 Within Groups 2.138 27 0.079 Total 3.8 29 Table 6. Multiple comparisons of impact strength between groups using Tukey HSD. A multiple comparison test in Table 6 showed a statistically signiUicant difference between control and 9% TTO, and 6% and 9% TTO (P < 0.05), while between control and 6% TTO there was a non-signiUicant difference (P > 0.05), which explains why the 6% had no effect on the impact strength of high-impact acrylic. (I)Group (J)group Mean Difference(I-J) Standard Error P-value Control 6% TTO 0.125 0.12583 0.587 9% TTO 0.55 0.12583 0.000 6% TTO 9% TTO -0.425 0.12583 0.006